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| Questão | Responda |
| Energy can never be __________ or __________, it can only be ______________ from one _____ to another. | Energy can never be CREATED or DESTROYED, it can only be TRANSFERRED from one FORM to another. |
| Energy can only be used when it is transferred from one form to another. This is called ______. | Energy can only be used when it is transferred from one form to another. This is called WORK. |
| When work is done some of the energy is transferred into __________ forms, while some of the energy will be transferred into _________ forms. | When work is done some of the energy is transferred into USEFUL forms, while some of the energy will be transferred into WASTE forms. |
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| A light bulb is supplied with a total of 150J of electrical energy. The bulb gives off 60J of light energy. Calculate the percentage efficiency of the bulb using the equation: | Percentage efficiency = (60 ÷ 150) x 100 Percentage efficiency = 40% |
| How much energy does a 150W light bulb transfer in: a) three seconds b) one minute | The POWER of an electrical appliance tells us how much electricity it transfers in one second. Power is measured in Watts (W). 1 Watt = 1 Joule of electrical energy transferred per second. 1 W = 1 J/s a) energy transfer = power x time energy transfer = 150 x 3 energy transfer = 450J b) a) energy transfer = power x time energy transfer = 150 x 60 energy transfer = 9,000J |
| A 2,500 W electric heater is switched on for 4 hours. Calculate the energy used in that time and the cost of using the appliance if 1 unit costs 9 pence. | E = P × t where: E is the energy transferred in kilowatt hours, kWh P is the power in kW t is the time in hours. Power = 2,500 W = 2.5 kW Energy used = 2.5 × 4 = 10 kWh Cost = 10 × 9 = 90 pence |
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A 200W TV is used for an average of 3 hours each day.
Calculate how much the TV costs to run per week.
Cost of 1 unit =
10 pence.
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Tv (binary/octet-stream)
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E = P × t where: E is the energy transferred in kilowatt hours, kWh P is the power in kW t is the time in hours. Power = 200W = 0.2kW Energy used = 0.2 × (3 x 7) = 4.2 kWh Cost = 4.2 × 10 = 42 pence |
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